The Trump administration has unveiled what could be its most environmentally consequential rollback — even among the many environmental rollbacks it's attempting– dramatically weakening auto emission and fuel efficiency standards.

And there are few places that would feel that consequence more than Connecticut.

With motor vehicles contributing about two-thirds of standard pollutants to the state's notoriously bad air and about 40 percent of its greenhouse gas emissions, any rollback could stall or even reverse the delicate progress that's been made on both.

"It couldn't be any worse from our perspective," said Rob Klee, commissioner of the Department of Energy and Environmental Protection. "These are the worst choices for an administration that only makes the worst choices for the health and safety of our elderly and our children."

Since just about the moment it came into office, the administration through the Environmental Protection Agency has telegraphed its desire to undo the dramatically tightened mileage standards of 50 miles per gallon the Obama administration put in place for cars and light-duty trucks for the 2022-2025 model years.

"The question all along has been how crazy and bizarre they would be," Klee said. "They chose as crazy and bizarre as they could."

The Trump administration offered several options, but its preferred one would hold mileage at 2020 levels of about 35 miles per gallon through 2026. It also wants to hold greenhouse gas emissions at 2020 levels for that time period.

But more drastically, it wants to rescind what's known as the California waiver – the caveat baked into the Clean Air Act since 1970 that allows California to set its own stricter motor vehicle emissions standards. The most recent waiver, issued in 2013, covers standard pollutants, greenhouse gas emissions and allows the state to have a zero emissions vehicle (ZEV) sales mandate to achieve those goals.

Other states are allowed to use the waiver and more than a dozen do – accounting for more than one-third of the vehicles in the country. Connecticut is one of them, seeing all three tighter levels as a way to keep both standard pollution and smog down and, more recently, as a way to minimize greenhouse gas emissions.

Thursday's action is widely expected to unleash a torrent of legal action that could tie up the process for years, leaving automakers in a limbo they are not happy about.

Connecticut had already joined a group of states signaling they are prepared to fight rollbacks to the auto standards. Attorney General George Jepsen Thursday was among 20 attorneys general issuing a broad statement reasserting that commitment to fight what the statement called a "reckless and illegal plan."

Specifically for Connecticut, Jepsen said in a statement: "As a downwind state, Connecticut struggles to maintain our air quality, and lessening standards for passenger cars and light-duty trucks nationwide will only exacerbate the problem. My office will continue to work with our partners in other states to aggressively fight this administration's assault on clean air."

No waiver among the more than 100 California has received has ever been rescinded and it's legally unclear if or how that can happen. Any number of legal scholars are arguing that the EPA may be on shaky grounds based on arguments it presented.

Under Connecticut's Global Warming Solutions Act, greenhouse gas emissions are mandated to be 10 percent below 1990 levels by 2020, and on their way to 80 percent below 2001 levels by 2050. Greenhouse gas emissions briefly dipped below the 2020 target in 2012, but have been creeping back up since, according to data and projections by the environmental advocacy group Acadia Center.

With just about every coal and most oil-burning power plants in New England closed, and the whole region participating in the Regional Greenhouse Gas Initiative to cut power plant greenhouse gas emissions, there's little the state can do to cut electric sector emissions further. So the key tool Connecticut has to work with to cut emissions on its own are vehicle emissions.

Klee said the state's current modeling for greenhouse gas emissions reduction strategies assumed that the existing federal standards would remain in place. Now his department has to figure out the exact impact the rollbacks would have on meeting the emissions targets.

Relaxing efficiency standards means vehicles will use more fuel than they would have under the Obama standards, so that's likely to have an impact on standard pollutants and the smog and poor air quality to which they contribute.

The state remains consistently in "non-attainment" with the 2008 ozone standards. That will intensify as the stricter 2015 standards kick in. If emissions levels are frozen, improvement becomes that much more difficult.

Ozone exceedence days in recent years have gone down – 32 in 2015, 31 in 2016, 20 in 2017, and 14 so far in 2018.

Under the ZEV mandate, which Connecticut participates in with seven other states including California, the goal for the state is 150,000 zero emissions vehicles by 2025. As of the most recent reporting on Sept. 1, 2017, there were 5,576. There is no federal ZEV standard, so if the waiver is successfully rescinded, the program disappears.

Area environmental groups wasted no time expressing their displeasure with the EPA proposal, warning of the dire consequences on Connecticut but also pointing out that the proposals now face a 60-day comment period and could change.

"It certainly would be awful if it went through," said Emily Lewis, a policy analyst at Acadia Center. "It would have a big impact on Connecticut emissions, but there are a lot of steps before we get to that point."

While the emissions and fuel efficiency standards are interrelated, there are actually two sets of regulations. Emissions standards were put in place to address the brown clouds of the 1960s as result of standard car pollution. The EPA regulates that.

The mileage standards — also known as the Corporate Average Fuel Economy (CAFE) standards — were put in place in the mid 1970s to address the high gasoline prices of the Arab oil embargo. That is regulated though National Highway Traffic Safety Administration (NHTSA) in the Department of Transportation.

The California waiver only applies to emissions, not the CAFE standard. Until the Obama administration, the two were handled separately.

Just before the Obama administration began some important changes occurred. A U.S. Supreme Court ruling allowed greenhouse gas emissions to be added to the suite of emissions the EPA could regulate as part of auto emissions – making them eligible under California's waiver as well.

The Obama administration decided to handle the emissions and efficiency standards – both up for review for the 2011-2016 model years – together. They did that again for the 2017 to 2025 model years – the ones the Trump administration is trying to rollback. Those negotiations, which included the auto industry, California and others, resulted in essentially a national emissions standard.

The proposed rollback already risks setting up a two emissions standards, with California expected to announce its separation from the federal emissions standard later this month.

The Trump administration is basing its argument on safety, claiming among other things that less efficient cars will prompt people to drive less, resulting in fewer accidents. It is also arguing that the rollback will keep car prices down, allowing people to afford new, safer cars. And it argues that the rollback will have little impact on emissions.

"Our proposal aims to strike the right regulatory balance based on the most recent information and create a 50-state solution that will enable more Americans to afford newer, safer vehicles that pollute less," said Acting EPA Administrator Andrew Wheeler in a statement. "More realistic standards can save lives while continuing to improve the environment."

Those arguments sound familiar to Claire Coleman, an energy attorney with Connecticut Fund for the Environment. She was on the Democratic staff of the U.S. House Oversight and Government Reform Committee that reviewed the 2011 and 2017 standards and heard the same things from Republicans back them.

"The arguments are not surprising and they're also not convincing," she said. "They made claims of safety and claims of consumer impact then and both of those justifications have been proven wrong."

For Connecticut, however, Coleman said what she's worried about with the rollbacks and rescinding of the waiver – which she thinks will not stand up in court – is the environmental impact.

"We need all the tools in the toolbox to tackle transportation emissions including lowering emissions in traditional gas cars and transitioning to ZEVs as soon as possible," she said. "This rule threatens to take away those critical tools."